Peromyscus truei
pinyon mouse

Pinyon mice can be found as far east as the panhandle of north Texas and as far west as the Pacific coast. The northern limit of their range is central Oregon, and the southern limit is southern Mexico. (Hoffmeister, et al., 1981; Wilson and Ruff, 1999)

Pinyon mice are terrestrial mammals that can be found at altitudes ranging from sea level to elevations of greater than 2300 meters. They frequent arid or semi-arid climates, preferring brushland and desert, and are typically found near pinyon junipers, hence their common name. However, pinyon mice can also be found in open, grassy habitats, as well as landscapes including canyons, redwoods, yellow pine belts, sagebrush, scrub oak, boulders, cacti, and rocky slopes. Pinyon mice are able to endure warm, dry summers in addition to snowy winters. They make dens under rock ledges, outcrops, stone shelves and slabs, and in live or dead trees. (Hall and Morrison, 1997; Hoffmeister, et al., 1981; King, 1968; Wilson and Ruff, 1999)

Pinyon mice have long, silky fur that ranges from yellow-brown to dark gray on the back and fades to white on the under parts and feet. They may or may not have a pectoral spot. The tail is tipped with long hairs and has a dark dorsal stripe running down its length. The hind feet are large, and are typically 22 mm or more in length. Juveniles have gray pelage that changes with a series of molts, starting at 7 weeks and finishing at 10 to 11 weeks of age. Coat color matches the habitat regionally, allowing these mice to blend into vegetation and hide from predators. Males and females are similar in size, the average weight is about 20 g, and the head and body length ranges between 171 to 231 mm. Tail length varies from 76 to 123 mm. The size of pinyon mice often varies with location; pinyon mice in the western parts of their range tend to have a longer tail, smaller body size, smaller ears, and smaller hind feet than their counterparts in the east. (Hoffmeister, et al., 1981; King, 1968; Wilson and Ruff, 1999)

Pinyon mice have a promiscuous mating system in which females nest in small territories and males seek mating opportunities with nearby females. (Ribble and Stanley, 1998)

Although mating can occur in all seasons, pinyon mice breed primarily from mid-February to mid-November with a peak between April and June. Females give birth to a litter of three to six pups after a gestation period of approximately 26 days, though gestation may be as long as 40 days if the female is lactating. Females first come into estrus at approximately 50 days of age, and males are capable of inseminating females at approximately 9 weeks of age. (Hoffmeister, et al., 1981; King, 1968; Scheibe and O'Farrell, 1995; Scheibe, 1984; Wilson and Ruff, 1999)

Newborn pinyon mice weigh around 2.3 grams at birth, and they are born completely hairless with their ears and eyes folded shut. The pups are capable of squeaking at one week of age, and their bodies are covered in hair by day 14. The pups nurse for three to four weeks, at which point they become independent. Females exclusively care for their young in a nest until they are weaned. (Wilson and Ruff, 1999)

The lifespan of pinyon mice and other mice in the genus Peromyscus has not been studied in detail. An individual Peromyscus maniculatus lived to be eight years old in captivity, but studies have shown that mice in this genus rarely live more than a year in the wild. Only 20% of the young in each nest will survive their first year of life, and only 2-3% of adults live long enough to breed in consecutive seasons. (Hoffmeister, et al., 1981; King, 1968)

Pinyon mice are nocturnal rodents that sleep periodically throughout the day. They are excellent climbers, frequently using their long tails for balance. Studies have shown that pinyon mice are more active foragers when ambient temperatures are higher. Pinyon mice are less active on moonlit nights, most likely because there is an increased risk of predation when it is brighter outside. In times of severe drought, pinyon mice can increase urine concentration, reduce the moisture content of their feces, and drop into a diurnal torpor to save energy. (Hall and Morrison, 1997; Hoffmeister, et al., 1981; King, 1968; Ribble and Stanley, 1998; Scheibe and O'Farrell, 1995; Scheibe, 1984)

Pinyon mice frequently use multiple den sites during the day. Male dens are typically farther apart from each other than female dens, but the territories of males tend to overlap each other more than the territories of females. In general, male territories are larger, while female territories are smaller because females are constrained to their dens during breeding. This reproductive constraint is the basis for their promiscuous mating system in which males must search for females. (Hall and Morrison, 1997; Hoffmeister, et al., 1981; King, 1968; Ribble and Stanley, 1998; Scheibe and O'Farrell, 1995; Scheibe, 1984)

Communication in pinyon mice hasn't been well-studied. They are likely to use visual, auditory, chemical, and tactile modes of communication.

Peromyscus species are known for their acute senses of hearing and smell, which they use to navigate, find food, and escape predation at night. Their enlarged eyes suggest they have a well-developed sense of vision in low light conditions. Their long whiskers are used for tactile perception.

Pinyon mice are primarily frugivorous and granivorous, although they will also readily eat insects, spiders, and other invertebrates. Adults typically feed on juniper seeds (Juniperus) and berries in the winter and acorn mast (Quercus) in the summer. Pinyon mice are notorious at caching their food supply; they frequently dig holes and bury their food in various places around their territory, particularly around den sites. These cache networks may become quite extensive. Finally, pinyon mice are capable of surviving on a very limited water supply, which is crucial to their survival in the arid habitats they occupy. (Hoffmeister, et al., 1981; King, 1968; Wilson and Ruff, 1999)

Predation on pinyon mice has not been well studied, although predation most likely plays a role in the high mortality rate of these rodents. Their primary predators are owls, diurnal birds of prey, and snakes, especially rattlesnakes. They escape predation by remaining inactive during the day in dens, by their cryptic coloration, and by their acute senses at night. (King, 1968)

Pinyon mice are almost always found near pinyon junipers, hence their common name. Juniper seeds are the main food source of pinon mice, making them, like other members of the genus Peromyscus, significant predators of conifer seeds. Thus they impact their communities by impacting the composition of the plant community. Their seed caching behavior may also result in germination of seeds. Pinyon mice are also an important and abundant source of prey for many avian and mammalian predators. (King, 1968)

It is not known whether pinyon mice have positive affects on human populations, aside from their important ecosystem roles.

Pinyon mice serve as an important reservoir for several types of parasites. Some have speculated that they are capable of carrying plague-infested fleas, but this has not been well documented. Members of the genus Peromyscus are capable of carrying chiggers, a common pest, as well as the ticks that transmit Rocky Mountain Spotted Fever and Lyme disease to humans. Peromyscus species are also important reservoirs for hantaviruses. (King, 1968)

Pinyon mice are not currently threatened throughout much of their range. However, since pinyon junipers are a crucial part of their habitat, destruction of such habitats can imperil these mice. The subspecies Peromyscus truei comanche, found in the pandhandle of northwestern Texas, is considered near threatened by the IUCN. (King, 1968)